A Study In Emerald
by LostPipersChild
Summary: Based on a study in pink, Sherlock and John are in their final year at Hogwarts and attracting the attention of Slytherin girls, Lilly Potter and muggleborn Gwen Williams. When a student is found dead and Harry Potter himself can't seem to solve it, guess who steps in to 'help'.
1. Chapter 1

Chapter One

After six, uneventful, adventure-free years at Hogwarts, I don't think any of us were expecting something like this to happen. I mean, why would we? Lilly was perfectly used to living in the shadow of her famous parents and by now the shock of her sorting had been forgiven by, well, everyone. But I say, so what? So she ended up in Slytherin why does that automatically make her bad? I turned out ok after all, and I'm muggleborn! Contrary to popular belief, it can happen. Being in Slytherin doesn't mean you have to be evil, it just means you have ambition and a hope for something better. I know I had big plans, and so did Lilly.

I suppose it started on our very first day back after the holidays. I was sitting with Lilly at the Slytherin table when she nudged me in the ribs.

"Hey Gwen, what do you know about that guy over there?"

I looked up to gaze at the boy she was nodding at. He was sitting at the Gryffindor table talking to a Ravenclaw boy and a Hufflepuff girl. He was fairly good-looking with sandy hair and a serious expression. I recognised him and smiled ruefully.

"Forget it Lilly, that's John Watson. You know Mary in Hufflepuff? She has a total crush on him and she'd scratch your eyes out if you as much as look at him."

That was another myth, it wasn't just Slytherins who could be bitches. Lilly frowned in disappointment.

"I know who he is! I just wanted to know his relationship status."

"If I've said it once, I've said it a thousand times, wizards need Facebook!" I sighed. "It would avoid all this confusion."

Six years of being best friends had taught Lilly to just ignore me when I started talking about muggle stuff. She sighed regretfully and went back to her toast. I shook my head, smiling, and glanced up at John again. The boy he was talking to suddenly looked over and for a second our eyes met. Blushing, I dropped my gaze. I knew that boy, Sherlock Holmes. He was a bit of a weirdo but very handsome. With only forty people in the whole year it was almost impossible not to know everyone's names by now but Sherlock was someone I'd never had much interaction with. I remembered his brother Mycroft had been head boy when we first arrived and the two had famously never got on. Other than that he was a bit of a question mark. A total shit in classes, winding all the teachers up by being a little smart arse but other than that he kept himself to himself.

"So how did you enjoy France?" I asked Lilly just for a distraction. She shrugged.

"Alright, aunt Hermione kept trying to tell us about the history, you'd love it."

"I probably would, you're aunt's great! I loved it when she came in to give that lecture about Elf Rights last year."

Lilly rolled her eyes and patted my hand.

"Stick to history Gwen, leave the politics to me."

"Yes Miss future Minister for Magic." I said sarcastically before checking my watch and getting up. "And speaking of history, I've got it now. See you!"

Lilly waved me goodbye as I left the Great Hall and hurried up the marble staircase. History of Magic had got a lot better since Professor Weasley had started coming in every so often to take classes. Bill was something of an idol to me and had promised to help me get a job with Gringotts as a tomb-breaker at the end of this year. Today however Bill was nowhere to be seen and the only teacher present was Professor Bins. Slightly disappointed, I dropped into my usual seat and took out my books. The NEWT History class was traditionally tiny and this year only three were still taking it. Myself, Sherlock Holmes and the new head boy, James Moriarty.

Usually both of them completely ignored me but today Sherlock leant across to mutter,

"Tell your friend that Mary is sleeping with the Hufflepuff Quidditch captain so John's free."

I stared at him in surprise but then remembered that Sherlock had a tendency for knowing things that he ought not to. I sorted out my face into an expression of calm.

"Thank you, she'll be really glad. Why are you telling me?"

"Because John's being morose about it and it's getting on my nerves, so he needs distraction."

I bristled and glared at Sherlock.

"Lilly is not a distraction!" I hissed angrily. "And anyway, I know John, I know he wouldn't just use her as some fling."

Sherlock shrugged and sat back in his chair looking supremely disinterested. Grumpily I set about copying down notes for the rest of the lesson, though I did notice out of the corner of my eye that Moriarty was smirking. Well I'd never liked the guy anyway, always a bit creepy. But by the time I'd left History and was heading for Charms I'd decided to pass on the message to Lilly anyway (though leaving out the distraction part). Charms was much more full and under cover of the noise I told Lilly the good news.

"But how do you know? No offence Gwen but I'm always the one who hears gossip first!" Lilly whispered as she waved her wand absently. The water we were supposed to be turning into wine sloshed around in her glass. Catching the glass before it fell I said,

"A little birdy told me."

"Who?" asked Lilly curiously and I tapped the side of my nose.

Lilly was intrigued for a little while but as our first week back wore on she lost interest. All the energy she had that was not directed at school work was now being channelled into landing John Watson. This seemed to amuse Sherlock no end and endless hours were spent with me and him standing by in corridors whilst our friends chatted. However time for flirting was severely limited by the beginning on the Quidditch season. I couldn't believe that September had already slipped me by unnoticed and it frightened me. I had got so comfortable at Hogwarts these past few years that it was a shock to think I wouldn't be here much longer.

John played Seeker on the Gryffindor team so he was at practises three times a week. Not that I kept track of the Quidditch schedule of course, it was Lilly who kept giving me updates.

"And he barely has time to talk anymore!" Lilly told me fretfully one rainy evening three weeks before Halloween when we were both sitting in the library.

"Hmm." I said, not paying attention since I was glued to the Daily Prophet. Lilly scowled and peered at the front page.

"What are you so fascinated by anyway?" she asked irritably and I glanced up.

"There's been another disappearance in Hogsmeade, Carl Powers, remember him? Flunked out last year."

"Oh yeah! Didn't he get into big trouble for turning up to an exam hung-over? I think Dad's working on that case, mum said something about in the letter I got this morning."

It was no wonder Lilly wanted to go into the Ministry next year I thought, what with her father and her uncle working as Aurors, not to mention her campaigning aunt. It was a surprise that neither of her brothers had been remotely interested in politics. James who had left three years ago played Chaser for some team or other, and I didn't have a clue what Albus was up to. Just then Sherlock Holmes sauntered over and sat down with his pile of books.

"I suppose you're discussing the murder in Hogsmeade." he said, opening a volume on advanced potion making. I stared at him curiously but Lilly looked up eagerly.

"Do you know if John will be off any time this week?" she asked, foregoing her dislike of Sherlock. He gave her a withering look.

"Do you really want me to repeat what you already know? You have memorised John's training timetable off by heart."

Lilly looked affronted but I had to silently agree with Sherlock. Ignoring him I turned to her and said in exasperation,

"Look, why don't you just ask him out already? Arrange to meet in Hogsmeade or something."

"I can't just ask him out just like that!" she said, looking shocked.

"Why not? He obviously likes you back and I'm getting bored of hanging around in corridors. I'm getting behind on my school stuff!"

"And her mother is badgering her." Sherlock chipped in and I goggled at him.

"How the hell did you know that?" I asked incredulously.

"It's quite obvious, your left hand says it all."

Both of us stared at him so he elaborated, pretending to be bored but quite clearly enjoying showing off.

"The ink stains on your left hand are from a muggle pen so you've obviously been writing home a lot. The letter sticking out of your bag is on muggle paper and slightly crumpled up so it clearly annoyed you, and your eyes are tired suggesting you've been staying up late trying to finish homework. Now you have the handwriting of a generally lazy person who doesn't usually do more work than absolutely necessary so at a guess I'd say you're under pressure from your parents, more likely your mother whom I hear is a teacher and therefore very concerned with your school work."

We stared at him a little while longer until I said,

"That's really cool."

"Really? That's not what people usually say."

"What do they usually say?"

"Piss off."

I snorted and Lilly muttered,

"That what I'd say."

"Yeah you can piss off about the lazy thing but the rest was really spot on. How do you notice all that?"

"Observation, the rest of you people are all so unobservant."

I was fairly sure that he had just insulted me but at that moment John came in and sat down, firmly closing the current conversation and prompting a new one taking place solely between himself and Lilly. I didn't mind, I had an essay to finish anyway.

Sherlock's words grated at me for the next few weeks until I found myself thinking about him as I lay in bed at night, hardly a good sign. I didn't like being called ignorant, which was effectively what he had done, and I racked my brains for a way to disprove his theory. For some reason I kept going over the conversation in the library. Something about it didn't quite ring true, something Sherlock had said. But it wasn't until Halloween that I got a chance to try and prove my worth. The feast was going well as usual, live bats kept getting tangled in girls hair and the Bloody Baron drifted by unnervingly a couple of times. Lilly and I was holding our annual argument about the muggle version of Halloween.

"I just don't see the point of celebrating something you don't believe in!" Lilly said, waving a cookie shaped like a spider at me impatiently.

"It doesn't matter if you believe in it!" I countered. "Halloween is just an excuse for kids to dress up and beg for sweets, and for adults to dress up and get drunk out of their skulls!"

Just then I noticed Professor Longbottom hurry up the staff table to the Headmasters chair. He whispered in Professor Slughorn's ear urgently and the portly old man paled considerably. It was only noticeable from where I sat because his face was usually a ruddy shade of red behind his sizably moustache. He spoke with Longbottom a little longer before standing up to address the students.

"Ah, and incident has occurred, ladies and gentlemen, and I would like you all please to return to your common rooms immediately. Prefects take charge, if you will."

There were moans of protest and a fair few calls for an explanation. But the teachers had all risen as one and were trooping out of a side door. I watched them go with a mixture of intrigue and excitement. Unobservant eh?


	2. Chapter 2

Chapter Two

"Gwen I don't think this is a good idea!" Lilly hissed as we hurried along the deserted top corridors. Everyone else was being shepherded to their common rooms but we had given them all the slip a few floors back.

"Come on Lilly, don't you want to know what's going on?" I whispered excitedly as we came to a corner and slowed down to check it was clear.

"Not particularly, what makes you think the teachers are up here anyway?"

"That door they went through, it only leads to the north wing of the seventh floor which hasn't been used for years! Why else would they come here? I'll show him who's unobservant."

Lilly stopped short and stared at me in disbelief.

"Is that what this is about?!" she demanded. "For Merlin's sake Gwen! Just let it go!"

"I will not let it go! I'll show that upstart little prat."

"Anyone I know?" asked Sherlock as he and John came through a secret passage hidden behind a tapestry. Lilly and I jumped out of our skins and I growled,

"Jesus Christ Sherlock! You scared the living daylights out of us! What are you doing here anyway?"

"At a guess I'd say we were doing the same thing as you two, checking out the crime scene."

"How do you know it's a crime scene?" Lilly asked still clutching at her heart like she might have a seizure. Sherlock raised an eyebrow.

"Didn't you see Professor Longbottom's knees?"

"What- oh never mind, I'll just take your word for it." I sighed. Sherlock nodded.

"Probably for the best, you wouldn't understand anyway."

I opened my mouth to yell at him but he had already moved off down the corridor with John in tow. Grinding my teeth angrily, I tugged Lilly after them.

"Sherlock it's bad enough that you drag me into this kind of stuff over the holidays!" John said. "Can't we just forget about it when we're at school."

"Not when something happens right under our noses, no." Sherlock countered, then he threw out an arm and caught John in the chest. We all stopped and edge towards the corner where we could hear voices. Sherlock flattened himself against the wall and peered around, making it impossible for any of us to do the same. I could hear Professor Slughorn's voice which sounded distressed.

"…terrible, terrible! No idea she was so unhappy!"

"Well it certainly looks like suicide again." said a man's voice and Lilly clapped a hand over her mouth, her eyes wide. She shoved Sherlock out of the way so she could get a look. I ducked down and popped my head out just below hers. Practically all the teachers were standing in the dusty, badly lit corridor, as well as several people in maroon robes. The one who was talking to Slughorn had messy black hair and wore glasses, and he looked very familiar.

"Hey, isn't that your dad?" I asked Lilly in an undertone and she jabbed me in the back to shut up.

"I suppose we should let the Law Enforcement Squad take over then." said Harry Potter, looking over his shoulder sadly at an old classroom. Slughorn nodded and slowly the adults trickled away until only one was left guarding the cordoned off class. Just then someone spoke behind us and we all whipped around.

"Well why aren't I surprised to find you here freak?"

The woman was dark skinned and dark haired, and she was looking at Sherlock with pure loathing. Sherlock didn't look at all abashed.

"Hello Donovan."

Her lip curled and she prodded us around the corner into the corridor. The man guarding the class looked up and groaned.

"Oh Jesus, what is _that_ doing here?"

"Don't talk Anderson you lower the IQ of the whole school." Sherlock countered and we snorted. Lilly was looking from Donovan to Anderson with a frown.

"Hey…I remember you two!" she cried suddenly. "Weren't you the ones who got caught snogging in the potions class?"

Both adults blushed scarlet and I saw Sherlock smirk. Anderson glared at Lilly.

"Oh I know you! You're Potter's kid aren't you?" he sneered. "So Sherlock's sidekicks are getting famous are they?"

Just then another, older man came around the corner and called,

"Well if it isn't Sherlock Holmes and John Watson, I had a feeling I'd be seeing you."

"What's the situation Lestrade?" Sherlock asked, ignoring the exasperated expressions on Donovan and Anderson's faces. Lestrade reached us and looked grim.

"Sixth year girl, Kelly Trent, found by the caretaker an hour ago in that classroom, looks like suicide."

Lilly and I both exchanged appalled glances.

"Kelly's dead?!" I cried, making everyone look at me. "But why would she kill herself? And how?"

"For once, not a bad question." Sherlock said calmly. "How did she 'kill herself'?"

"Poison, draft of living death."

"Hmm, not the usual choice for a student suicide." Sherlock mused. "Difficult to get a hold of to start with."

Lestrade regarded Sherlock for a moment before sighing heavily.

"Why couldn't it for once just be a straightforward suicide? Alright, go on, but only five minutes this time, ok?"

"Please, I'll be done in two." Sherlock scoffed and he swept past the stunned Anderson and Donovan in the classroom. Not wanting to be left behind, the rest of us followed him. I had to swallow hard when I saw Kelly's prone body lying on the floor. She was a chubby Hufflepuff girl who took great care how she dressed. The hem of her robes had pink stitching around it and she wore a number of ugly rings on her fingers. Sherlock circled the body with his eyes narrowed. He knelt down to peer at Kelly from every angle whilst we stood back quietly. I leant over to whisper to John,

"Uh, does this sort of thing happen to you a lot?"

"You have no idea." he muttered. "Whenever something weird happens back in our town you can bet he's there like a shot. We've met the Magical Law Enforcement Squad more times than I can count."

"So that's why Donovan and Anderson hate you?" Lilly asked and Sherlock answered without looking up.

"No, they hate me because I might have told everyone about their affair, Anderson's fiancée wasn't pleased."

I scowled at him whilst Lilly rolled her eyes.

"You go out of your way to wind people up don't you? Can't you keep our deductions to yourself once in a while?"

"Why should I do that?" asked Sherlock curiously before pointing at the floor in front of Kelly. "Now why would she scratch that into the floor I wonder?"

We edged around to see what he was pointing at. Scratched onto the stone floor was a single word '_Rache_'. Kelly's glasses lay next to it so she had obviously used them to scratch the word.

"What does that mean?" I asked as John knelt down beside Sherlock.

"I don't know, it may be German for revenge." Sherlock mused as John rubbed the message with his finger. I frowned thoughtfully and cocked my head to one side.

"That's a bit farfetched don't you think?"

Sherlock look up at me slowly and John shook his head frantically behind his back. But I was determined to voice my opinion.

"Kelly didn't even speak German, I doubt she knew how to write it. It looks more like half a word, but she died before she finished it."

Lilly scrutinized the word and nodded slowly.

"Yeah, it looks like Rachel or something."

Sherlock opened his mouth but then closed it again, glancing between the word and us. John snorted.

"Bloody hell I think you've silenced him, you deserve a medal or something."

With Sherlock still struggling to think of something to say, John bent down to examine Kelly.

"Dead…no longer than an hour." he muttered. "Definitely_ looks_ like suicide."

Before he could go on a tall figure appeared at the door and there was a sharp intake of breath.

"What do you four think you're doing?!" asked Professor McGonagall furiously.

I had never been in the headmaster's office before and I hoped never to repeat the experience. All four of us had been hauled up here by a seething Professor McGonagall and we now stood, heads bowed and shame faced before Professor Slughorn. At least, Lilly, John and I were, Sherlock was looking distinctly bored by the whole affair. The office was quite full, our heads of house were there, as well as Mr Potter and Mr Weasley. Lestrade stood looking guilty behind all of them. McGonagall began the assault.

"Explain yourselves!" she spat, glaring at us with her hawk-like eyes. I flinched and John began to apologise on behalf of all of us. It wasn't good enough for McGonagall.

"Have you no respect Watson?! Sneaking around a suicide scene when you had been expressly told to go to your-"

"It wasn't suicide." cut in Sherlock and everyone looked at him. Mr Potter frowned at him.

"What makes you say that?" he asked sharply. Sherlock glanced around to ascertain that he was the centre of attention before going on.

"Kelly Trent wasn't the brightest egg in the basket, she would have the skill to make a Draft of Living Death and anyway, didn't anyone see her eyelids?"

Everyone looked blank so he elaborated.

"Her eyelids were creased, a sure sign of the imperious curse."

"You're saying she was forced to kill herself?!" Lestrade piped up incredulously but Potter shook his head.

"You can't Imperio someone to kill themselves, the survival instinct is too strong."

"But it proves that her death wasn't as simple as it seems!" Sherlock persisted. "And who is Rachel?"

I glanced at him indignantly but chose not to say anything.

"What does Rachel have anything to do with this?" Ron Weasley asked in confusion.

"That's what she was scratching into the floor. A family member or a friend perhaps? Lestrade get someone on it."

Several of the adults bristled at being given orders by a seventh year kid and John wisely trod on Sherlock's foot.

"It is not up to you to solve mysteries Mr Holmes." Slughorn said sternly. "From now on you are to stay out of this or I'll contact your brother."

Sherlock winced before nodded moodily. Slughorn fixed the rest of us with a steely look.

"As for the rest of you, I expected better. Off to bed with all of you and this had better be the last escapade do you hear me?"

We turned and left the office in silence. The moment we had reached the corridor downstairs however, Sherlock said,

"Idiots. They didn't notice the crucial thing!"

"What?" Lilly snapped, her face as red as her hair. Sherlock smiled a rare smile.

"Kelly was missing a ring."


	3. Chapter 3

Chapter Three

The next day we were all sitting in the battered old armchairs in the corner of the library. Madam Pince was stalking the Restricted Section so for a few moments we were alone.

"Ok." I said, closing my Ancients Runes book and fixing Sherlock with a shrewd gaze. "Ok, you've been dying to tell us all day, what does Kelly's missing ring have to do with anything?"

Sherlock took his time, dotting an i in his essay and turning the page of his book. But eventually he looked up at us and began talking like we had been in the middle of a lengthy discussion.

"Kelly Trent wore rings on every finger but one, she took it off and planted it on her killer."

"She might just have lost it!" said John in exasperation but Sherlock shook his head.

"The skin was red and swollen around the area where the ring used to sit so she had it before she put on weight and didn't remove it very often, so clearly a dear possession. She deliberately took it off to lead us to her killer. What do we know about Kelly Trent may I ask?"

We glanced at each other and he rolled his eyes.

"Come on! Data, I can't make bricks without clay. Tell me what you knew about Kelly Trent."

"Well…" I began slowly, thinking. "She was in sixth year, Hufflepuff, uh…"

"Yes yes we know this from yesterday!" Sherlock said, clicking his fingers impatiently. "What else?"

"She was muggleborn but raised in care." Lilly jumped in. "Not a very happy childhood I don't think, and then there was that horrible boyfriend of hers."

"What boyfriend?" Sherlock asked looking distracted and Lilly and I raised our eyebrows.

"Don't you keep up with gossip in this place?" I asked smugly. "Kelly and Mark Davis have been going out for two years now! And he's the biggest control freak you ever met, he's in our house, total twat."

"Ah…" said Sherlock, closing his eyes as if he'd just realised something. "Of course, unhappy relationship, hence the weight gain. And that meant she had a string of lovers."

"So you do keep up with gossip." Lilly said.

"No, just a deduction. So possessive boyfriend, unhappy background, certainly seems like a mix for suicide."

"But you think it was murder." I said and then something popped into my head, something that had escaped my notice for weeks.

"Carl Powers!" I cried, making John and Lilly jump.

"Sorry?" said John in puzzlement.

"Carl Powers!" I repeated, staring at Sherlock. "You said, ages ago, you said he'd been murdered."

"Of course he was, but the Ministry put it down to suicide." said Sherlock, going back to his essay. I shook my head tiredly.

"I'm not even going to ask how you know that." I sighed. "So you think there's a connection between Kelly and Carl?"

"They both were murdered but their deaths were put down to suicide." Sherlock shrugged. "But other than that I see nothing that connects the two victims."

"They both liked to stick their noses in other people's business." Lilly snorted. "Not like you mind, more like cheap gossip."

"Are you four still talking about that then?" asked Mr Potter as he stepped out from behind a bookshelf. Lilly looked mortified.

"Dad! We were just - " she began but Mr Potter put up a hand.

"Relax Lilly, this isn't nearly as bad as what we got up to at school."

He dropped into the seat beside his daughter looking exhausted. Sherlock was eyeing him with a calculating expression.

"Have you found Rachel?" he asked and Potter shook his head.

"No, Kelly had no family and we can't find a record of either of her parents. None of her friends are called Rachel, or anyone who might have a connection to her."

Sherlock's eyes narrowed and I sat back in disappointment. Potter was looking at Sherlock with an odd expression, it was almost like amusement.

"Professor McGonagall has been telling me all about you lot." he suddenly chuckled, nodding at Sherlock. "You're a bit of a wild card aren't you? Too clever for your own good according to half the Law Enforcement Squad."

"Well half the Law Enforcement Squad are too stupid for their own good." Sherlock sighed, flicking through his textbook boredly. Potter gestured at John.

"And I hear you've already got one foot in the door of St Mungo's. They'll be glad to have you they're short on staff."

"Well I – I still haven't decided yet." John said awkwardly. Finally Potter turned to me.

"And you're Bill's protégée, he's promised to give you a reference at Gringotts hasn't he."

"Um, yes sir."

Potter nodded and contemplated each of us thoughtfully for a while before saying,

"Now look you lot, I know Slughorn warned you off and Lilly, your mother told me to warn you off too, but personally I think Hogwarts is well due a new crew of misfits."

We gaped at him in shock (all expect Sherlock who sighed yet again and didn't lift his eyes from his work) and Potter smiled.

"Don't do anything dangerous of course, but put your heads together and you might just be able to solve this for me. The case has officially been closed but I'd like to hear from you if you come up with anything."

And with that he kissed Lilly on the forehead and got up to leave. For the next few days I took Potter's request very seriously and I racked my brains for an answer until Lilly was sick of discussing it. She started accompanying John down to his Quidditch practices and I spent increasingly uncomfortable amounts of time with Sherlock. We didn't talk as such, just sat in the library, occasionally throwing out ideas to one another. Sherlock kept focusing on the missing ring, whilst I was intrigued by who Rachel might be. He seemed convinced that Kelly, a girl who knew how to be cautious because of her many affairs, had deliberately planted the ring on the killer. Somehow this was supposed to lead us to him but I couldn't for the life of me see how, unless he or she was stupid enough to start wearing the ring so that we could conveniently notice it.

The first Quidditch match of the season was upon us before I had time to blink and as always it stirred up much excitement. Well, it did for everyone else, personally I couldn't give a damn if Slytherin were beaten until they cried. Lilly was committing treason this year in supporting Gryffindor for John's sake and as always, Sherlock didn't even seem to notice anything was going on. It seemed odd to me that someone who noticed the tiniest details could be ignorant about something as huge as Quidditch.

"I'm not ignorant I'm just not interested." he said when I asked him about it on the morning of the match. Lilly was going to watch the match but with the rain coming down hard, Sherlock and I were once again heading for the library.

"Do you think we spend too much time in here?" I asked quietly as we took out our books and Madam Pince glared suspiciously at us.

"You do, I share my time between here and the potions lab." Sherlock muttered. "Did I tell you that I discovered that mice continue to create saliva after they die?"

"Ah no, and I have no wish to know either." I said curtly.

Gryffindor won the match by a narrow margin and the usual after match party was scheduled. For the past five years everyone had finally realised that a party was not something to be confined to a single house common room and that the presence of booze transcended all differences. The whole school knew about the party so of course the teachers were clueless. Lilly and I turned up at the Room of Requirement just a few minutes before curfew ended and we were met by a cheery John.

"Shame this place isn't a secret anymore." I said wistfully, glancing around the huge yet cozy room. People from the upper three years were milling around whilst House Elves scurried between everyone's legs baring trays of fire-whisky.

"How about some music!" called some Ravenclaw kid over the heads of the crowd. "Weird Sisters?"

There were groans and laughter and I shouted back,

"Oh yeah, if you feel like stepping back twenty five years! Put something new on!"

Disgruntled, the Ravenclaw stuck on a song popular in the wizarding charts and people started to dance. As I was not yet sufficiently drunk I skirted around in search of something other than whisky. Locating the butterbeer, I made a beeline for it and met Sherlock standing moodily in the corner.

"Isn't it past your bedtime Einstein?" I asked, sipping on my beer and Sherlock smiled sarcastically.

"Hilarious. I see you're really hitting the bottle tonight, do you think you finish the _whole drink _this time?"

I stuck my tongue out and leant against the wall.

"Anymore thoughts on the Kelly Trent case?" I asked, scanning the room to see where Lilly had got to and spotting her in another corner snogging John. _About bloody time_, I thought. Sherlock looked disgruntled.

"No, we need more information! That ring, that's the key."

"Why do I feel like we've had this conversation a million times? Forget the ring! The only way to track an object that small is if it had a chip in it or something, and stuff like that doesn't work at Hogwarts! I say we concentrate on Rachel."

Sherlock looked like he wanted to argue but I jabbed him in the ribs and pointed across the room.

"Look! That's Kelly's boyfriend, maybe we should go and talk to him."

Sherlock wrinkled his nose but I dragged him along after me. Davis was sitting at a table alone, surrounded by empty bottles of whisky and he looked up at us blearily.

"What?" he asked aggressively and I felt my mouth grow dry.

"Uh, hi." I said, in a slightly higher voice than usual. "We wanted to ask you about Kelly, we were friends of hers see?"

Davis' eyes filled with tears and he spat,

"Piss off! I don't want to talk about it."

"So Mary's boyfriend is in the hospital wing then?" said Sherlock suddenly and Davis glared at him.

"Oh don't pretend you worked that out, someone told you!"

"Indeed, your deodorant did."

"My deodorant?"

"Yes, it's for men."

"Well of course it is! I'm wearing it!"

"So is Mary." said Sherlock coolly, jabbing his thumb over his shoulder at the girl in question. Davis paled and he didn't look quite so drunk anymore.

"What do you want to know?" he asked shakily.


	4. Chapter 4

Chapter Four

"I knew she was cheating on me!" Davis said through gritted teeth once we'd sat down uninvited across from him. "I just knew!"

"You and the rest of the school." I snorted. "But never mind that now! We want to know if anyone had any motive to kill her."

"Besides yourself of course." added Sherlock. Davis glared at him and banged the fist holding his wand on the table.#

"And what's that supposed to mean freak?" he hissed. I leant back a little and Sherlock rolled his head to look at Davis.

"You have the most obvious motive for killing her." he said. "I'm surprised it didn't cross the minds of the Aurors, dull witted as they are it was a big thing for them to miss. And you can put that away because attacking us will only cast further suspicion on yourself."

Davis' face slackened and he began to shake. Sherlock looked wholly unconcerned.

"Lucky for I know you flunked your potions OWL so couldn't possible make a potion like the Draft of Living Death without blowing yourself up. So, who else had a motive?"

"No one." said Davis pathetically. "She was always winding people up, gossiping and everything, but not enough to make someone want to kill her!"

"Well she must have gossiped about something worth killing for." said Sherlock impatiently.

"It might have something to do with Rachel." I said and Davis' head jerked up.

"What her mum?" he said and my eyes grew wide in excitement.

"How do you know that's what her mum's name was?" I asked eagerly. "Mr Potter couldn't find a record of her parents."

"Kelly had this ring with _Rachel_ engraved on it." Davis shrugged. "She kept banging on about it belonging to her mum, she never took the damn thing off!"

"This is a waste of time." Sherlock hissed, dragging me out of my chair and away from Davis.

"Sherlock its her mother! How can you think that's not important?"

"Oh come on! She wrote that as she was dying, she would have been in pain, Rachel is a code for something I know it!"

"Or it could just be that she was thinking about her dead mum!" I snapped.

"But she died years ago why would she still be upset?" asked Sherlock. He watched my exasperated expression for a moment before saying, "Not good?"

I shook my head and Sherlock blinded, before shaking himself irritably.

"Forget about Rachel, we need to think who could kill Kelly. The murderer would be someone who hunts in a crowd, who can move around the school unseen, in plain…sight."

Sherlock trailed off and he stared into space for a while. Then he said quietly,

"Oh that's clever, yes very clever, and no one would suspect…"

"Suspect what?" I asked sharply and Sherlock seemed to snap out of his trance.

"I, I'll tell you tomorrow. I think I'll just go to bed."

"What?! But it's not even ten yet!"

"I hate it when John drags me to these things, I just want to go to bed!"

And with that he hurried out of the room. I watched the wall melt into place behind him before sighing and turning to look for Lilly. It was only a few minutes later that I realised someone had been standing outside the door when Sherlock left, and how stupid I had been.

Argus Filch was standing in the shadows outside the Room of Requirement waiting for Sherlock. As the wall closed and the loud music and talking was cut off behind him, Sherlock gazed at the middle aged caretaker in his shabby over coat and shuffling shoes.

"Kelly Trent and Carl Powers worked it out didn't they?" he said coolly and Filch's mouth stretched into an unpleasant grin.

"They always were too clever for their own good." he wheezed. "And they paid for their nosiness."

"How did you get them to go with you?" Sherlock asked and Filch laughed.

"Not here Mr Holmes, how about somewhere more secluded eh? Set the scene why don't we."

Sherlock didn't even hesitate; he followed Filch without a care in the world. Filch took him to a lonely tower overlooking the lake. At the top of the narrow winding staircase was a dusty room with a table and two chairs facing each other. On the table were two bottles, full of inky black potion.

"Of course I don't get the little brats myself." said Filch casually, lighting the candle with a match. "Can't perform the Imperious Curse. You know why I suppose?"

"You're a squib." said Sherlock impassively, gazing around the threadbare room. Filch shot him a poisonous look.

"You're another one who's too smart for your own good, but at least you don't laugh. That girl laughed, and that stupid boy."

"So someone brings them to you, takes their wand and leaves them to be punished." Sherlock deduced. "Who takes them?"

"Ah now, that's not for you to know sunshine. I saw you, strutting around the school like you owned the place, you and your little backing singers. Thought you were so clever didn't you?"

"Oh I don't think, I know." said Sherlock and Filch grimaced.

"Well you're not that smart see!" he growled. "Now sit down, we're going to play a little game."

Sherlock sat and so did Filch. Sherlock's eyes were flicking between the two bottles, calculating, deducing.

"I suppose your contact provides the potion as well." he said. "My my he must be bored."

"Something you two have in common." Filch sneered. "He pays me for every kill I make, I intend to be rich when I retire and you snot nosed little brats have had this coming for years."

"So one bottle contains poison the other a fake, how do you make the students drink one?"

Filch took a gun out of his pocket and pointed between Sherlock's eyes. Sherlock looked fleetingly disappointed.

"Ah, dull." he sighed. "You can't use magic so you resort to muggle weapons. Not exactly ingenious."

"Does the trick." Filch shrugged.

"No it doesn't, I took advanced muggle studies in my first year I can tell the difference between a real gun and a fake."

"Yeah but I wouldn't need it anyway would I?" said Filch, stowing the gun away. "For the same reason I didn't need to take your wand. You just want to prove just how clever you are, you'll pick a bottle without a fuss."

"One thing I don't understand is why the choice?" asked Sherlock, studying his fingernails. "Why not kill them and be done with it?"

"My contractor." Filch explained. "He wouldn't pay if it was dull, and this way I can make it look like suicide. But enough dawdling Holmes, chose."

Sherlock dropped his eyes to the bottles again and after a moment, tapped the one on the left. Filch leant forward and stared at Sherlock shrewdly.

"Care to test it?" he asked softly.


	5. Chapter 5

**I can't believe the response I've had with this! Thank you so much for your reviews, you've encouraged me to write more along this plot line **

Chapter Five

"I'm telling you he's worked it out!" I panted, taking the steps two at a time with John and Lilly in tow. We halted at the top of the stairs and pressed ourselves against the wall to let a teacher go past, it wouldn't do for them to find out about the party. Once they were gone we hurtled out into the corridor.

"Gwen stop for a second!" John gasped, grabbing my amr and pulling to to a halt. "We can't just run around without a clue where we're going! Sherlock might have just gone back to Ravenclaw Tower!"

"John, please, since when does Sherlock elect to go to bed? You have to tell him when to eat and change his shirt! You didn't see him, he's worked out who the murderour is and he's gone after him all alone, he's in danger!"

"Well how are we supposed to find the murderer? Unless you've got a magic tracking device we're screwed." Lilly said, clutching a stitching in her side. I bent down and rested my hands on my knees, and then smacked my hand to my forehead.

"The ring!" I cried, comprehension dawning on me. "The bloody ring! Kelly would want to find something as precious as that if she ever lost it, so she put a tracking spell on it! Does anyone know how to do that?"

"I can." said John, frowning, "But you need a key word to use in the spell, something to link it to the object."

Lilly looked at me and the same excitement I could feel bubbling up inside me was visable in her eyes too.

"Rachel!" we both cried in unison. John needed no further encouragement. He whipped out his wand and held it in the palm of his hand.

"_Cacumino Rachel_!" he said, and the wand spun in his hand until it pointed towards the Grand Staircase at the far end of the corridor. We all pause for the tiniest fraction of a second, before running like the wind for the stairs. The wand kept spinning in different directions as we re-positioned ourselves until, somewhere on the fifth floor, we had to stop and consult it properly. It was now pointing to our left, right into the wall.

"Well what does that mean?" asked Lilly in confusion. I looked out of the window at the grounds and gasped.

"Oh, look!" I chocked, and pointed through the glass towards a tower level with our corridor. There, in the top room we could see Sherlock and Mr Filch, the psychopathic caretaker, sitting at a table. Sherlock was reaching for a bottle that even from here looked ominous.

"He's never going to drink it!" Lilly gasped. But Sherlock was uncorcking the bottle, rasing to his lips!

"No Sherlock!" I screamed though I knew he couldn't hear me. John raised his wand and said firmly,

"Get out of the way Gwen!"

I leapt aside and John took a steady shot at Filch through the window. His red spell smashed a hole in our window, sped across the twenty foot gap between us and the tower, shattered the second window and caught Filch in the back of the head. Filch jerked violently off his chair onto the floor and Sherlock leapt to his feet. He stared at Filch for a moment before looking up at us. For a second, we just watched each other, then I did quite a bizarre thing. I waved.

"So you really have no idea who shot the spell." said Mr Potter, his eyebrow raised and his arms folded. We were in the Entrance Hall and the whole place was filled with Law Enforcement guys and teachers. Medi-wizards kept coming up to us and trying to check us over for injuries. We all shook our heads innocently. The four of us were sat in a row on the very bottom steps of the Grand Staircase and through Mr Potter's legs I could see Donovan glaring at us. Somehow the sight cheered me up a lot.

"And I suppose you were all just sleepwalking and happened to come across Filch and Sherlock in a locked room at the top of the tower?" Harry added, his mouth quivering like he was fighting not to smile. Sherlock looked up at him, frowning.

"Look, we're in shock, we've got blankets and everything!"

He plucked at the woollen blankets the medi-wizards had insisted on draping over our shoulders. Harry threw up his hands in a peaceful gesture.

"Alright alright, I'll leave you to recover, I have a lot of paperwork to fill out."

He turned and left us to sit in silence. We watched as Filch's body was carried past on a stretched and a chill ran down my spine. He had hit his head as he landed on the stone floor and blood had leaked into his brain. The medi-wizards said he had an undetected brain tumour which had caused extensive damage, go figure. The stretcher was taken out into the grounds where a chilly mist was leaking into the Hall. After a pause John said, without turning to Sherlock,

"You were going to drink that damn potion weren't you?"

"What gave you that impression? I had the situation totally under control."

All three of us turned our heads slowly to glare at Sherlock with matching expressions of incredulity. He gazed steadily back and we couldn't help ourselves, we laughed.

"We shouldn't be laughing!" Lilly chuckled. "It's crime scene!"

"Go on then, admit it." I said after we'd calmed down. Sherlock frowned at me.

"Admit what?"

"Admit that you were wrong about Rachel, admit that knowing a bit about human sentiment is useful."

"No I won't, I realised who was behind it all without needing to know who Rachel was. All I needed was cool logic."

"Oh and where did your cool logic lead you exactly? To the receiving end of a poison!" Lilly said angrily and Sherlock shrugged.

"I could tell it wasn't the real poison, child's play."

Before any of us could shout him down, James Moriarty came sauntering up to us. He was in his dressing gown so he'd obviously just been woken up but I could see the tell tale signs of confetti in his hair. Another secret party goer it seemed.

"Not a bad job boys and girls." he drawled and we eyed him suspiciously. He was watching us with a curious expression, it was something like hunger and I didn't like it. He was looking at Sherlock in particular.

"Very impressive work Sherlock, I'm sure your brother will be very proud."

Sherlock grimaced and Moriarty chuckled softly.

"Professor McGonagall asked me to escort you back to your dorms but your big kids now, I think you can take yourselves."

We understood this as a dismissal and we got up to leave, Lilly and I for the dungeons, the boys for their respective towers. We were almost to the stairs when Moriarty called,

"Try not to trip over any more murders on your way to bed now."


End file.
